High public debt damages economies – and it’s more than just a theory

Paul Ormerod is an economist at Volterra Partners, a visiting professor at University College, London, and author of Positive Linking: How Networks can Revolutionise the World.

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Paul Ormerod

THE distinguished American academic economists Carmen Reinhardt and Ken Rogoff have been very much in the news. Their 2009 book This Time is Different was a comprehensive examination of financial crises over the past 800 years, and the work received many plaudits and awards. They suggested that, when the ratio of public debt to GDP in a country rose above the 90 to 100 per cent range, the chances of a financial crisis increased sharply. And the consequence was that economic growth in the country would be adversely affected.

The finding has been queried by a trio of fellow Americans. Reinhardt and Rogoff do seem to have conceded that their own calculations contain a glitch, and the new analysis has been seized on by opponents of austerity policies. But how much does it matter that an error was made? At the moment, the debt to GDP ratio in the UK is just below the crucial level of 90 per cent. Does this miscalculation mean that George Osborne should change tack and spend to try and stimulate the economy?

In defence of Reinhardt and Rogoff, they never elevated their suggestion into a “theorem” or a “law”. They simply suggested that high levels of public debt tend to be a Bad Thing. Even the most devoted Brownite would surely accept that there is some limit to how much public debt can be incurred relative to the size of the economy. The real question is: what is this limit?

A great deal depends upon the extent to which an increase in debt leads to higher interest rates. More public expenditure financed by issuing long-dated gilts at around the current yield of 2 per cent is one thing. But if extra spending causes gilt yields to rise to, say, 4 per cent, it is pretty disastrous.

Higher interest rates would have an adverse effect on business confidence. If rates doubled, the capital value of the outstanding stock of gilts held by the private sector would fall by 50 per cent – a severe negative shock to the wealth of the sector. And higher taxes will at some point be needed to meet the higher interest payments.

There is a lot of evidence to suggest that high public debt levels relative to GDP are indeed associated with higher interest rates. The Mediterranean economies are just the latest example of this. But there is no automatic connection between debt and rates. The relationships which are coaxed out of the data are not like the laws of physics.

So much depends upon psychology. Osborne pushing up debt by cutting taxes might be one thing. Ed Balls doing the same by hiring more bureaucrats might be perceived quite differently. But at some point, regardless of who the chancellor might be, an increase in public debt would have an adverse impact on the economy. The theoretical channels by which this happens are well understood. And an ounce of good theory is worth a ton of applied econometrics.

Paul Ormerod is an economist at Volterra Partners, a director of the think-tank Synthesis and author of Positive Linking: How Networks Can Revolutionise the World.